Puzzling shared dna matches

[suecee]

I have several Ancestry dna matches who have no other shared matches with me. Yet some of them crop up many times as the only shared match of someone else. e.g. KU (20cM match) has 39 people so far for whom she comes up as the only shared match. SH (20cM match) comes up as the only shared match for 33 other people.

What does it mean when someone, like KU or SH, does not have any shared matches with me despite being the sole shared match for quite a large number of people (none of whom have any common ancestors with me).

Am I just missing a critical shared match who might provide the connection, what is going on?

Thanks for any enlightenment.

[CorleyMiller]

I have something similar, around 30 of my matches all each have the same single match (a lady in Virginia) in common with me, I have no idea who any of them are or how they fit in to my tree.
With 21,000+ matches, there are bound to be some statistical quirks. but I think that Anc's 20cM matches cut off policy also has to be borne in mind here. I have many thousands of matches for whom Anc shows no shared matches, they may exist but are not shown as such as they're less than 20cM. Contrast with MH and their much lower cut off, I've just looked at my smallest match there and we have 61 shared matches. I'd guess that if Anc had an 8cM cut off like MH the situations you're seeing would be somewhat different.

     

[suecee]

That makes sense if the connection is way back. I may not ever have any shared matches closer than 20cM for KU and SH or maybe a 20cM+ match may come in the future that at least allows me to know which side of the family to put them on.
Or they may all be connected to any one of the illegitimate ancestors I know I have, (or didn’t know I had) and I’ll never know which one.

[Rosinish]

Glad this post came up as I have similar with no other matches, no clue to which side, line, area or country.

I don't see what benefit it is to ancestry to cut off at 20 cMs but it's certainly of no benefit to us 

Annie

[melba_schmelba]

I have several Ancestry dna matches who have no other shared matches with me. Yet some of them crop up many times as the only shared match of someone else. e.g. KU (20cM match) has 39 people so far for whom she comes up as the only shared match. SH (20cM match) comes up as the only shared match for 33 other people.

What does it mean when someone, like KU or SH, does not have any shared matches with me despite being the sole shared match for quite a large number of people (none of whom have any common ancestors with me).

Am I just missing a critical shared match who might provide the connection, what is going on?

Thanks for any enlightenment.

Because the people who match you and KU or SH match you at less than 20cM. But when you look at these smaller matches below 20cM, KU and SH show up because they match this smaller match at 20cM or above and you match KU and SH at 20cM or above.

Glad this post came up as I have similar with no other matches, no clue to which side, line, area or country.

I don't see what benefit it is to ancestry to cut off at 20 cMs but it's certainly of no benefit to us 

Annie

In theory, in very homogenous groups like Ashkenazi Jews, Amish or Mormons, you can end up having 1000s of shared matches if you lowered the limit and Ancestry decided it would be misleading as the closeness of match implied may be misleading, but it is probably also to do with the cost of computer servers and data for Ancestry .